1. Field of the Invention
The present invention relates to an ink jet recording apparatus, and more particularly to an improvement in a system for searching the phase of ink droplet production.
2. Description of the Prior Art
In an ink jet recording apparatus of charge control type, a piezoelectric element mounted on an ink ejecting nozzle is energized with a high-frequency voltage to make the nozzle vibrate, and thus the ink ejected from the nozzle is changed into ink droplets in synchronism with the waveform of the high-frequency voltage. A charging electrode is disposed in the vicinity of a region where the ejected ink changes into ink droplets, and a phase searching signal is first applied to the charging electrode. Then, the electric charge of an ink droplet which has been electrified by the phase searching signal, is detected to search the phase of ink droplet production. Thereafter, a recording signal synchronized with ink droplet production is applied to the charging electrode, and thus the electrification of ink droplets is controlled by the recording signal. A deflection electrode is disposed on the flying path of the ink droplets, to deflect the flying ink droplets in accordance with the electric charge thereof. A collector is disposed on the flying path of both an ink droplet which has been electrified by the phase searching signal, and an ink droplet which has not been electrified by the recording signal, to collect (or catch) these ink droplets. While, an ink droplet which has been electrified by the recording signal, flies clear of the collector, and is then deposited on a recording medium.
In the ink jet recording apparatus of this kind, in order to record an accurate image on a recording medium, it is required to accurately control the electrification of ink droplets. Accordingly, it is necessary to adjust the time each voltage pulse of the recording signal is generated, so as to match the time each ink droplet is produced. The above-mentioned phase searching signal is used for such a phase adjustment.
As disclosed in a U.S. Pat. No. 4,016,571 to T. YAMADA and a U.S. Pat. No. 4,121,223 to H. Omori et al., the phase of ink droplet production can be known in such a manner that the electric charge of an ink droplet electrified by the phase searching signal is detected by an induction-type or collision-type sensor which is provided on the flying path of the ink droplet. In such a method, however, the sensor is disposed between the deflection electrode and recording medium, and therefore there arises a problem that the flying path of ink droplets becomes longer and the deviation of flying path is increased. In order to solve this problem, various methods have been proposed in which the phase of ink droplet production is detected on the basis of a change in a current due to charged ink droplets. In one of these methods, as disclosed in, for example, a Japanese Patent Application (Publication No. 8460/1978), a voltage is applied between the ink in the nozzle and the charging electrode, and the phase of ink droplet production is detected by a change in a current flowing through the charging electrode. In this method, however, owing to a useless leakage current flowing through an ink supply system, there is a danger of ink being subjected to electrolysis at the connecting point of the ink and a power source for detecting the production of ink droplets, and thus changing in quality. In another one of the above methods, as disclosed in a Japanese Patent Application (Laid-open No. 12226/1979), the phase of ink droplet production is detected by a change in a current flowing through the nozzle. In this method, however, noise generated in an ink supply system by external disturbances is introduced into a detection circuit, and thus a detection error is increased.